April Preston refuses to waste any calories on anything that doesn’t taste amazing, a trait she picked up from her farmer father. She grew up eating and drinking the produce from the farm – milk, clotted cream, poultry and vegetables – a lifestyle she describes as idyllic. In fact, she didn’t drink pasteurised milk until she was 16.

She’s a bit unusual in the food industry in that she has experience across all three major sectors, from foodservice to retail to manufacturing. She started off in restaurants, working front of house at everywhere from Bibendum with Simon Hopkinson to Terence Conran’s Pont de la Tour, as well as with 90s pioneering modern British chef Stephen Bull.

Preston then spent almost two decades at M&S and had a hand in around 15,000 product launches, before joining the board at 2 Sisters Food Group.

Now, as Harrods executive head of food innovation, she is overseeing a “taste revolution,” as she calls it – a mammoth four-year overhaul of the food halls, which up until 2017 hadn’t been touched in three decades.

Personalisation is forefront for the luxury retailer, and nothing is too much for the customer. Preston gives the example of a pair of visitors that Harrods makes a cake for every six months. The twosome want to share a dessert, but don’t like the same flavours. As a solution, the department store makes them a cake that has the same vanilla base, but with one half iced in peanut and the other half in mango. It’s this kind of philosophy that is driving change in the food halls.

On a walk around the first redeveloped food hall, Preston tells Food Spark about the transformation, new products that have been rolled out, how veganism is having an influence and her dislike of food being made Instagram-worthy but not necessarily tasty.

I grew up on a farm in Devon and it was a dairy farm. When you have access to the most incredible ingredients at a very young age, you can’t go backwards from that.

That’s still my philosophy today: you have to start with the right ingredients, then you can create something fantastic.

I started working when I was 12. I started on a farm picking up eggs – it wasn’t my own farm, it was a different farm – and then I quickly graduated from there. When I was 14, I worked in a tea room in Exeter.

If you count when I started when I was 14, I had 13 years in the restaurant industry on and off at different levels, then I had my experience at M&S in food retail, and then I went into food production. So really this job here has brought all those three elements together in one place and it’s really exciting for me.

I was at M&S for 18 years. It’s such an incredible business to work for because there was never once in those 18 years that I ever woke up and thought, ‘I’m a bit bored of this.’ It’s such a big business. You can move around to different categories, and again it was such a good groundwork for coming here as I worked in every single category there.

I’ve always got a really soft spot for Indian and Chinese ready meals. That was my first job as a product developer, when they didn’t really exist in this country. It was very pioneering at that time, because nobody had heard of regional Indian cooking and nobody had heard of South East Asian food. Introducing the British public to some of those cuisines was really interesting.

I think we must have launched Thai and South East Asian five or six times before it really stuck at M&S. It’s a timing thing, and that’s a big part of being successful. I think one of the things you have to tell yourself is that if something hasn’t worked, it’s not that it isn’t right, it just might not be the right time.

I’m a big believer in [not giving] up on things too early, just put them back in the cupboard for a few years and bring them out again. I think that’s proved right time after time. I think even regional Indian, I launched twice before it stuck, and it’s just about timing. If we all had that magic wand and crystal ball, then we could get it right every time.

I wanted to see the food world from a different perspective when I went to 2 Sisters. I had restaurants and retailing; I wanted to see a bit about food production, and now I’m so glad that I did because, while it’s a very different scale here – I have 150 chefs rather than 56 factories – the mentality of food production is one you can transfer across different industries.

I’m always into work before seven and I stop off at the little Roast and Bake – that is one of the first things I launched when I came here. We launched it last August. I can’t start the day unless I’ve stopped off there and had a little cortado.

I do try and make sure I walk the floor four or five times a day because I do want to observe what the customers are doing, how they are interacting with the food – there is so much you can learn just from watching.

[Harrods is] the only ever one-store operation that I’ve worked in. Obviously M&S had 750-plus stores, and 2 Sisters had 56 factories, and I’ve always been on the road a lot and visiting lots of different places, whereas here it’s a wonderful thing to have it all on your doorstep, including all the people you work with and all the things you are selling. It means you can be really pacey with the things you do and change things quickly.

As we go room by room we are redeveloping the whole product offer, but we are not throwing the baby out with the bathwater. If there is something amazing we leave it as it is, we don’t change for changes sake.

It’s a good opportunity to relook at everything and create new ranges. We didn’t produce any bread in-house last year, so that’s brand new, and the coffee range, the patisserie range. There were 750 new lines in the first room, and we delivered that between January and October [last year], so it was quite a mammoth task.

We decided what we wanted to be famous for first of all. So in the first redeveloped room it was bread, coffee, patisserie, some of the subcategories in grocery – honey, spices, olive oils and vinegars – and that was based on what our customers were already coming to us for. But what we felt we could really do well and differently, primarily based on our experts and what we knew.

It was a little bit chicken and egg actually, as on the bakery side we decided we wanted to create this amazing bakery and we found the master baker to populate it, whereas we have incredible tea and spice experts in the business and it was about really playing to their strengths.

Most of the innovations out there are things that I’m really proud of because the team came up with it. So the sourdough which is then personalised [you can have your initials baked into the bread for example] – that has been incredible. The honey that has been certified as organic, which is really hard as bees can fly anywhere.

One personal baby out there is that spice fixture, as I felt so strongly and I had such a clear vision of what I wanted it to be and how I wanted customers to interact with it. I think that is probably the one I’m most proud of, but the room is full of things that the team has come up with, and that’s what so wonderful about the environment. It’s such a creative environment, everyone sparks off each other.

In previous businesses I had product developers, but when you get a chef and a product developer together, then you get real magic.

It’s a rolling program. The next room to shut is the fresh hall, and that shuts in June and reopens in late autumn this year. We have just opened the wine room. There are some amazing, interactive experiences down there and some wonderful wines and spirits.

By the time we have done those first two rooms, as a local customer or a foodie customer you can pretty much do all your shopping that you would need to do to create anything in a normal week or for a dinner party even.

The other two rooms I can’t really give away, but they will be much more shopping for a special occasion, rather than an everyday purchase, and those will both open next year.

We are redoing all the restaurants and looking at those and getting new restaurants in. The thing with the restaurants is, people can spend a whole day here. It’s a million square feet, and what we need to make sure is that we offer something for every single occasion. So it might just be a quick coffee and a pastry or you might want something that is more lavish and destination based.

We have our finger on the pulse of the world food, but we are not a cutting-edge brand I suppose. People don’t come to Harrods and expect them to be first with everything. It’s not about being first, it’s about being best.

One of my philosophies is ‘simple things done really, really well.’ So I want the perfect sourdough loaf, I want the best coffee you can possibly drink, I want the best and most perfect honey you can select, and that is what is driving the selection and development of the products, rather than necessarily trends or innovation.

I think the move to veganism or vegetarianism will really heavily influence where wego as we open up the new rooms. But even on a personal level, if I had a crystal ball I don’t think it’s that many years before vegan becomes really mainstream – already it doesn’t have the stigma it used to have. I’ve got teenage children, and in their generation they have several friends who are vegan. When I was that age people would have been horrified.

I think what’s going to accelerate is this polarisation of how people shop. I think what we are starting to see now is people have a different mentality when they go to shop. They want to go somewhere and just do it really quickly and conveniently and just get what’s on their list – and maybe they do that online or do that in a store. But it’s all about convenience and getting in and out as quickly as you can; it’s all about a functional exercise.

At the other end of the spectrum, you’ve got a real experience. You go out and want to spend a day having an experience or maybe even a couple of hours, but it’s not just about going and getting your food, it’s about maybe eating something while you’re there – and it’s much more about what we’re doing here.

I was reading about Amazon’s first store that you don’t pay in, you just walk out and it takes your money, and I think that will also grow. So I think it will start to polarise, and you will see much more of the experiential side of it. And on the other side people will also be looking for ways to make it more convenient, quicker and less painful.

Harrods is all about personalisation – nothing is too much trouble. We’ve got the tea tailor: all of the tea and coffee you can taste and make your own blends. The coffees we roast here we can put in little coffee shop shells and we can personalise your loaves.

Fads affect my philosophy. One of the ones that annoys me is the Insta food thing, where it’s all about looking good and not necessarily tasting good, and it’s just there to be photographed and has lots of bright colours. I think there is a place for that, but not if you’re a real foodie. If you’re a real foodie it’s got to be style and substance, it can’t just be style, and I think that’s one of the fads that people will eventually go off.

Ingredients I cannot live without are capers and Kewpie mayonnaise. Literally anything that has that enhances it no end.